The typical style of switches used in harsh environments (such as in pools, spas, saunas, boats, industrial equipment, etc.) have heretofore included so-called membrane switches. In harsh environments, these membrane switches are often prone to degradation over time leading to product failure. Alternative switching systems often contain moving parts that tend to breakdown over time leading to product failure. Electronic capacitive sensors, on the other hand, are durable and can be used in place of mechanical and membrane switches as user input controllers. During use, capacitive sensors generate an electric field and define an active region in the electric field. The capacitive sensor then detects and switches state when certain objects, such as a person's finger, have entered the active region. Examples of capacitive sensors include touchscreen technology and capacitive sensors that are implemented as copper traces on standard printed circuit boards. In use, the operator places their finger (which is conductive) in the active region of a capacitive sensor causing a change in capacitance that is sensed by a control circuit. The control circuit than outputs a specific control signal in response to the sensed capacitance change which then causes a device such as a pump or heater to start or stop.
Pools, spas (sometimes referred to as hot tubs) and saunas are examples of wet environments in which user input controllers may be employed. Other wet environments in which user input controllers are employed include marine environments and environments where some types of industrial equipment are employed. In the case of hot tubs and saunas, the controllers are often placed within reach of the person that is using the hot tub/sauna. For example, a controller/control panel may be mounted in a cutout formed in the acrylic shell of a hot tub. In this situation, water can easily enter the active region of a capacitive sensor by splashing, condensation and/or transfer from the user, e.g. transfer from a wet user's hand.
There are at least two problems that can occur when capacitive sensors are used in a user input controller in a wet/harsh environment. First, water in the environment can cause a capacitive sensor to register false sensor readings (i.e. change states). This can happen when water, e.g. droplets, which is conductive, inadvertently enters the active region of the capacitive sensor. To overcome the problem associated with water entering the active region, the sensor can be calibrated to read a more precise range of capacitance change as an actual button press. However, this calibration to a more precise range of capacitance can generate a second undesirable consequence that often needs to be addressed. In more specific terms, once the capacitive sensor is calibrated to avoid false positives due to moisture, the highly calibrated sensors are often so sensitive that some people will have difficulty in triggering the switch. This can occur because every person has a different size, shape, conductance, and ultimately a different capacitance. Unfortunately, the capacitance generated by some people will be outside the calibrated range. These people will be unable to trigger such highly calibrated switches. This phenomenon is compounded in a wet environment because the capacitance measured can be affected when the user is wet.
In light of the above, it is an object of the present invention to provide a capacitive touch sensor assembly for use in a user input controller that can be used in wet and harsh environments without registering false sensor readings when water or other contaminants contact the assembly. Still another object of the present invention is to provide a capacitive touch sensor assembly that can be calibrated to avoid registering false sensor readings when water or other contaminants contact the assembly while allowing all users, regardless of their size, shape or conductance to operate the sensor assembly. Yet another object of the present invention is to provide a capacitive touch sensor assembly for use in a wet environment and corresponding methods of use which are easy to use, relatively simple to implement, and comparatively cost effective.